Spotted on mse and thanks to ramk_ for his post.
We went to Homebase today to buy wooden barrel planters for the garden.We had previously priced them at £19.99 each or 2 for £25. Today they were reduced to £9.99! BONUS!
We bought six and they went through the checkout for a total of £15!!!!
It seems the 2 for £25 takes £15 off every second one you buy, so when you buy two at £9.99 it still takes off the £15! ... so it's a fiver for every two you buy!